Hellblade: Senua’s Sacrifice: Save Game (Stories From the North Achievement and Bonus Cutscene)

To get it you need to collect all the runes.

The last rune is located near the save point.
Turn left, climb the stairs, left and along the corridor, then turn right and activate the rune.
Do not be alarmed, all the runes are already activated, but when you reactivate you get the coveted achievement.

Hellblade: Senua’s Sacrifice: Save Game (Stories From the North Achievement and Bonus Cutscene) Free Download

This cutscene is available only after collecting all the runes.
Just load your save and move forward.